Field of the Invention
This invention relates generally to rotating dynamoelectric machines and, more particularly, to such machines that receive power from a direct current or rectified alternating current power supply and that utilize electronic commutation means.
In conventional direct current rotating machines, commutation is essentially a mechanical switching operation to control the currents through the armature winding sections. This operation is accomplished in conventional machines with brushes and segmented commutators. In such constructions, the brushes wear and require frequent replacement. Sparking and its attendant generation of RF noise is also unavoidably present.
These disadvantages frequently prohibit use of DC motors in critical applications even though the use of such motors might otherwise be favored. Early attempts to provide brushless DC motors were mostly limited to: DC to AC inversion and, essentially, AC induction motor operation; use of rotor velocity for switching control but such control then was not effective at all rotor positions; or use of circuits having a larger number of switching devices with the result that the circuits for such devices were both complicated and expensive.
I have now devised simpler and less expensive DC motors and have recognized that different restrictions apply to electronically commutated motors than those that apply to mechanically commutated motors. Improved motor performance over the already good performance of conventional motor designs may be obtained by using a rotor position sensing system in conjunction with electronic switching, and a permanent magnet rotor in combination with a selected unconventional stator or armature winding arrangment for a direct current motor.
Motors embodying selected features of my invention are readily adapted for applications where space requirements are at a minimum. For example, such motors are readily adapted to drive the compressor of a recreational vehicle or automobile air conditioning system from the output of an alternator, or battery source. In such arrangements, an electronically commutated motor and compressor may both be sealed in a hermetic enclosure. In sealed arrangements, carbon pollution products are objectionable and use of brushless motors in such arrangements provides a distinct advantage over mechanical commutation. However, since the units are hermetically sealed, the reliability of the motor must be very good, and all parts of the motor must be such that refrigerant will neither damage the motor nor be damaged by motor components or the materials from which said components are made.
Conventionally, motor manufacturers have a first type of specialized equipment, processes, tools and dies, etc., for AC induction motors and a second type of the same for DC motors. To a great extent, such AC motor making, e.g., tools, etc., are not usable for present DC motor production. In accordance with another feature of the invention DC stators embodying the invention may be wound using conventional AC winding machinery.
Thus, another important advantage of the subject invention is the cost saving achieved both in manufacture and operation.
Electronic commutation may be achieved by either a bridge or star connection. The former improves copper winding utilization, while the latter offers the advantage of simplified electronics and by judicious selection of winding parameters, magnet size and electronics which controls the commutation cycle, there is obtained a reliable, highly efficient brushless DC motor having a desired speed-torque relationship which may be fabricated at a reasonable cost.